JPH0553067A - Lens for optical scan and optical scanner - Google Patents

Abstract

PURPOSE:To increase the degree of freedom for the arrangement of an optical sensor for synchronous detection for synchronization in optical scan. CONSTITUTION:A lens 4 arranged on an optical path between an optical deflector 3 and a plane to be scanned in an optical scanner which performs the optical scan by deflecting a beam of light from a light source device 1 in unmagnified angular velocity fashion by the optical deflector 3, and converging a deflected beam of light on the plane to be scanned by an image-forming lens as a light spot is formed in simplex structure by unifying an image-forming lens part 41 provided with a linearity correction function and which converges the deflected beam of light on the plane to be scanned with a lens part 42 for synchronous detection which converges the deflected beam of light on the optical sensor 8 for synchronous detection, and different image-forming characteristics are attached on the image-forming lens part 41 and the lens part 42 for synchronous detection, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens and an optical scanning device.

[0002]

2. Description of the Related Art An optical deflecting device for converging a light beam deflected at a constant angular velocity as a light spot on a surface to be scanned by an optical scanning lens to optically scan the surface to be scanned at a constant speed has been widely known. Has been. In such an optical scanning device, assuming a “virtual optical path” in which the light beam optical path from the light source to the surface to be scanned is linearly developed, the direction parallel to the main scanning direction on this virtual optical path is “main scanning compatible”. The direction that is parallel to the sub-scanning direction on the virtual optical path is referred to as the “direction”.

In the above-described optical scanning device, in order to align the scanning starting points of the optical scanning that is periodically repeated, the deflected light beam deflected to the optical scanning area is detected by the synchronization detection optical sensor and the synchronization detection signal is detected. Is generated, and the optical scanning is started a predetermined time after the generation of the synchronization detection signal.

In this case, it is preferable that the synchronization detecting optical sensor is arranged in the same plane as the surface to be scanned on which the light spot is formed by the optical scanning lens. This is because the deflected light beam is converged on a spot having a small diameter in the same plane as the surface to be scanned, so that the deflected light beam can be reliably detected even on the small light receiving surface of the synchronization detection optical sensor.

However, since a photosensitive recording medium such as a photoconductive photoconductor is generally arranged on the surface to be scanned, it is necessary to arrange an optical sensor for synchronization detection at a position where the arrangement of the photosensitive recording medium is not hindered. There is.

As a method for carrying out this, there is a method of "setting the deployment position of the optical sensor for synchronization detection apart from the optical scanning region within the same plane as the surface to be scanned". In the case of this method, There is a problem that the lens system in the main scanning corresponding direction of the optical scanning lens becomes large, manufacturing of the optical scanning lens becomes difficult, and the cost of the optical scanning lens increases. In addition, as another method, "a light beam condensed by an optical scanning lens is folded back by a mirror or the like, and an optical sensor is arranged at a position equivalent to a surface to be scanned (a position where an image of the surface to be scanned is formed by the mirror). Although there is a method, it requires an extra space for arranging the mirrors and the like, and from a practical point of view, there are large restrictions on the arrangement of the mirrors and the optical sensor for synchronization detection.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a novel optical scanning lens capable of increasing the degree of freedom of arrangement of an optical sensor for synchronization detection, and this optical scanning lens. An object of the present invention is to provide an optical scanning device using an optical lens.

[0008]

According to a first aspect of the present invention, there is provided an optical scanning lens comprising: "a light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is formed as a light spot on a surface to be scanned by an imaging lens. Optical scanning device that collects light and performs optical scanning ”
In, the lens is provided on the optical path between the deflector and the surface to be scanned. The optical scanning device is premised on not performing so-called "face tilt" correction in the optical deflector.

The optical scanning lens of claim 1 is a "single structure in which an imaging lens portion and a synchronization detection lens portion are integrated"
Have. The "imaging lens part" has the function of converging the deflected light beam as a light spot on the surface to be scanned and the linearity correction function, and the "synchronization detection lens part" collects the deflected light beam on the synchronization detection optical sensor. It has the function of lighting.
The imaging lens portion and the synchronization detection lens portion have different imaging characteristics. Here, “different image forming characteristics” means that the lens portions have different focal lengths and / or optical axes.

An optical scanning device according to a third aspect is an optical scanning device using the optical scanning lens as described above, which is a "light source device".
A "light deflector" for deflecting the light flux from the light source device at a constant angular velocity, and the "optical scanning lens" for condensing the light flux deflected by the light deflector on the surface to be scanned as a light spot, It has a "synchronization detecting optical sensor" for synchronizing the optical scanning.

As described above, the optical scanning device according to the third aspect is premised on not performing the correction of the surface tilt. Therefore, as the deflector, there is almost no surface tilt in principle, or a rotary polygon mirror whose surface tilt is corrected with high accuracy. It is desirable to use a pyramidal mirror or a hoso type mirror. The deflected light beam incident on the optical scanning lens of claim 1 may be a parallel light beam, a weakly divergent light beam, or a weakly convergent light beam. When the deflected light flux is a parallel light flux, the linearity correction function is a so-called fθ function, and the imaging lens portion is an fθ lens.

According to another aspect of the optical scanning lens of the present invention, "a light beam from a light source is imaged as a long line image in a direction corresponding to the main scanning, and an optical deflector having a deflection reflection surface near the image forming position of the line image is used. An optical scanning device that performs optical scanning by deflecting light at an angular velocity and converging the deflected light flux as a light spot on a surface to be scanned by an imaging lens "is provided on the optical path between the deflector and the surface to be scanned. It is a lens. The optical scanning device using this optical scanning lens has the function of correcting the "face-down" as described above.

The optical scanning lens of claim 4 is, like the optical scanning lens of claim 1, a unitary structure in which an imaging lens portion and a synchronization detection lens portion are integrated. The "imaging lens part" has a linearity correction function in the main scanning corresponding direction, and has a function of "making the deflection reflection surface position and the scanned surface position in a substantially geometrically conjugate relationship" in the sub scanning corresponding direction. The deflected light flux is condensed as a light spot on the surface to be scanned. The "synchronization detecting lens portion" focuses the deflected light flux on the synchronization detecting optical sensor. The imaging lens portion and the synchronization detection lens portion have different imaging characteristics.

That is, the image forming lens portion and the synchronization detecting lens portion have different focal lengths and / or optical axes at least in the main scanning corresponding direction.

An optical scanning device of a sixth aspect is an optical scanning device using the optical scanning lens of the fourth aspect. This optical scanning device includes a "light source device", a "line image forming optical system" for forming a light beam from the light source device as a long line image in the main scanning corresponding direction, and a deflection near the image forming position of the line image. An "optical deflector" that has a reflecting surface and deflects the light flux at a constant angular velocity, the above "optical scanning lens" that condenses the deflected light flux by this optical deflector as a light spot on the surface to be scanned, and the optical scanning It has a "synchronization detecting optical sensor" for establishing synchronization.

As described above, since this optical scanning device has a function of correcting the surface tilt, a normal rotating polygon mirror or the like can be used as the optical deflector. The deflected light beam incident on the optical scanning lens is divergent in the sub-scanning corresponding direction, but may be parallel, weakly divergent or weakly convergent in the main scanning corresponding direction. When the light flux is parallel to the direction, the imaging lens portion is a well-known anamorphic fθ lens.

In the optical scanning lens according to the first or fourth aspect, the image forming lens portion and the synchronization detecting lens portion may be separately formed of glass lenses, and these may be bonded to each other to form an integral body. It can also be configured as a single unit by molding with plastic (claim 2,
5).

The phrase "converging the deflected light beam on the synchronization detecting optical sensor" means that the deflected light beam converges on the light receiving surface of the synchronization detecting optical sensor at least in the main scanning corresponding direction. It is not always necessary for the deflected light flux to form an image on the light receiving surface.

[0019]

According to the present invention, as described above, the optical scanning lens is constructed by integrating the image forming lens portion and the synchronization detecting lens portion, but the image forming lens portion and the synchronization detecting lens portion are different from each other. Since it has image characteristics, the focal length and optical axis of the synchronization detection lens part are adjusted according to the desired position of the synchronization detection optical sensor to properly deflect the deflected light beam on the light receiving surface of the synchronization detection optical sensor. Can be focused on.

[0020]

EXAMPLES Specific examples will be described below with reference to the drawings. The optical scanning device shown in FIG. 1A is an embodiment of the optical scanning device of claim 6.

The light source device 1 is composed of a combination of a light source such as a semiconductor laser or a light emitting diode and a collimating lens, and emits a substantially parallel light flux. The radiated parallel light beam is focused only in the sub-scanning corresponding direction by the cylinder lens 2 as a line image forming optical system, and the main scanning is performed in the vicinity of the deflecting / reflecting surface of the rotary polygon mirror 3 as an optical deflector. An image is formed as a long line image in the corresponding direction and is reflected by the deflective reflection surface. The reflected light flux becomes a deflected light flux that is deflected at a constant angular velocity by the rotation of the rotary polygon mirror 3, enters the optical scanning lens 4, and converges toward the surface to be scanned. A drum-shaped photoconductive photosensitive member 5 is arranged on the surface to be scanned with the bus lines aligned with each other. Send to. The deflected light beam is detected by the optical sensor 8 for synchronization detection before each optical scanning,
Optical scanning is synchronized.

The optical scanning lens 4 has a unitary structure in which an image forming lens portion 41 and a synchronization detecting lens portion 42 are integrated as shown in FIG. 1 (b). Imaging lens portion 41
Is an anamorphic fθ lens and has an fθ function in the main scanning corresponding direction. Therefore, the light spot formed on the surface to be scanned by the imaging lens portion 41 optically scans the surface of the photoconductor at a constant speed.

The synchronization detecting lens portion 42 focuses the deflected light beam toward the synchronization detecting optical sensor 8. The optical sensor 8 for synchronization detection is arranged at a desired position between the optical scanning lens 4 and the surface to be scanned on the side of the optical scanning region on the optical scanning start side. The synchronization detection lens portion 42 is
The focal length is set according to the position where the synchronization detecting optical sensor 8 is arranged, and the deflected light beam deflected toward the optical scanning region is condensed toward the light receiving surface of the synchronization detecting optical sensor 8.

The synchronization detecting optical sensor 8 is, for example, a PIN.
Photodiode, etc., the diameter of the light receiving surface is 1-2 m
Since it is about m, the light-collecting state on the light-receiving surface may be such that light is condensed on the light-receiving surface region at least in the main scanning corresponding direction.

In this embodiment, the imaging lens portion 41
Has a function of correcting the surface tilt of the rotary polygon mirror 3 serving as an optical deflector, but the synchronization detection lens portion 42 does not necessarily have the surface tilt correction function. When the synchronization detecting lens portion 42 is not provided with the surface tilt correction function, the deflected light beam incident on the synchronization detecting optical sensor 8 fluctuates in the sub-scanning corresponding direction, and in some cases, detection failure of the deflected light beam may occur. It can happen. In order to avoid this, the light flux condensed on the light-receiving surface of the synchronization detection optical sensor 8 may have a long shape in the sub-scanning corresponding direction. For that purpose, the power of the synchronization detecting lens portion 42 may be made different in the main / sub scanning corresponding directions.

However, in the case of the embodiment described, the deflected light beam incident on the optical scanning lens 8 is a parallel light beam in the main scanning corresponding direction and is divergent in the sub scanning corresponding direction. Even if the lens portion 42 is configured as a spherical lens, there is no problem because the state of the light flux condensed on the light receiving surface of the synchronization detection optical sensor 8 becomes long in the sub-scanning corresponding direction.

The size of the synchronization detection lens portion 42 may be about 4 to 5 mm in the main scanning corresponding direction. Therefore, even if this portion is integrated with the imaging lens portion 41, the size of the optical scanning lens 4 is small. , Is not so different from conventional lenses.

The optical scanning lens 4 is formed by molding using plastic as a material. When molding a long and narrow lens such as the optical scanning lens 4, it is common to have a gate at the time of molding on one side in the longitudinal direction, and the accuracy of the lens surface tends to be asymmetric with respect to the optical axis. When the synchronization detecting lens portion is integrally formed at the end portion in the longitudinal direction of the image forming lens portion as in the present invention, the lens surface accuracy of the synchronization detecting lens portion is relatively higher than that of the image forming lens portion. Since it is rough, it is possible to effectively prevent the deterioration of the lens surface precision in the imaging lens portion by setting the gate on the side of the synchronization detection lens portion.

FIG. 2 shows only another characteristic part of another embodiment. In the case of this embodiment, the effective optical scanning deflection angle 2θ ₂ is larger than the effective deflection angle 2θ ₁ by the optical deflector 3, and the angle θ
₁₋ θ ₂ is relatively small. Therefore, the optical axis of the synchronization detection lens portion 42A of the optical scanning lens 4A is adjusted by the synchronization detection optical sensor 8 so that the scanning light is not “vignetted”, and the direction of the deflection light flux 10 for synchronization detection is adjusted. Is arranged away from the deflection area for optical scanning, and the position where the optical sensor 8 for synchronization detection is arranged is separated from the deflection area for optical scanning.

The embodiments of the optical scanning lens of claim 5 and the embodiment of the optical scanning device of claim 6 have been described above.
When the cylinder lens 2 is removed in the configuration of FIG. 1, an embodiment of the optical scanning device of claim 3 is obtained. In the case of this device, since the surface tilt of the optical deflector is not corrected, the rotary polygon mirror 3
In order to prevent surface tilt, a deflecting / reflecting surface or a rotating shaft with sufficiently high accuracy is used, or a pyramidal mirror or a hozo-type mirror is used as an optical deflector.

The image forming lens portion of the optical scanning lens may be an ordinary fθ lens having a lens surface which is rotationally symmetrical about the optical axis.

[0032]

As described above, according to the present invention, a novel optical scanning lens and optical scanning device can be provided. Since the present invention is configured as described above, the degree of freedom in the arrangement portion of the synchronization detection optical sensor for synchronizing the optical scanning is increased.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing only a characteristic part of another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light source device 2 Cylinder lens as a line image forming optical system 3 Rotating polygon mirror as an optical deflector 4 Optical scanning lens 5 Photoconductive photoconductor 8 Synchroscopic detection optical sensor 41 Imaging lens part 42
Lens part for synchronization detection

Claims (6)

[Claims] 1. An optical scanning device for performing optical scanning by deflecting a light beam from a light source at an equal angular velocity by an optical deflector, converging the deflected light beam as a light spot on a surface to be scanned by an imaging lens, and performing optical scanning. A lens arranged on the optical path between the scanning device and the surface to be scanned, which has a linearity correction function and focuses the deflected light flux as a light spot on the surface to be scanned, and the deflected light flux is detected synchronously. It is a unitary structure in which a synchronization detection lens portion to be condensed on a use optical sensor is integrated, and the imaging lens portion and the synchronization detection lens portion have different imaging characteristics. Optical scanning lens. 2. The optical scanning lens according to claim 1, wherein the entire lens is molded with plastic. 3. A light source device, an optical deflector for deflecting a light beam from the light source device at a constant angular velocity, and an optical scanning lens for condensing a light beam deflected by the optical deflector as a light spot on a surface to be scanned. And an optical sensor for synchronization detection for synchronizing the optical scanning, wherein the optical scanning lens is the optical scanning lens according to claim 1. 4. A light beam from a light source is formed as a long line image in a direction corresponding to the main scanning, and is deflected at an equal angular velocity by an optical deflector having a deflection reflection surface near the image forming position of the line image. In a light scanning device that performs light scanning by condensing a light flux as a light spot on a surface to be scanned by an imaging lens, it is a lens arranged on an optical path between a deflector and a surface to be scanned, Has a linearity correction function for the corresponding direction,
An imaging lens portion that has a function of making the position of the deflecting / reflecting surface and the position of the surface to be scanned substantially geometrically conjugate with each other in the sub-scanning corresponding direction and condensing the deflected light flux as a light spot on the surface to be scanned. And a synchronization detection lens portion for converging the deflected light flux on the synchronization detection optical sensor, which is a single structure, and the imaging lens portion and the synchronization detection lens portion are at least in the main scanning corresponding direction. An optical scanning lens having different image forming characteristics with respect to. 5. The optical scanning lens according to claim 4, wherein the whole is molded by plastic. 6. A light source device, a line image forming optical system for forming a light beam from the light source device as a long line image in the main scanning corresponding direction, and a deflective reflection surface near the image forming position of the line image. An optical deflector for deflecting a light beam at a constant angular velocity, an optical scanning lens for converging a light beam deflected by the optical deflector as a light spot on a surface to be scanned, and a light for synchronous detection for synchronizing optical scanning. An optical scanning device having a sensor, wherein the optical scanning lens is the optical scanning lens according to claim 4 or 5.